This invention relates to a data communication control sYstem in which transfer of data is carried out between two control units each of which has a microcomputer, and more particularly to a data communication control system of an electronic fuel injection control apparatus of an internal combustion engine, particularly a diesel engine, in which transfer of data is carried out between two control units.
Conventionally, a system for controlling the fuel injection of a diesel engine, in which transfer of data is carried out between first and second control units each having a microcomputer, has been disclosed, for example, in Japanese Provisional Patent Publication (Kokai) No. 61-1832. This system is so constructed that the first control unit is provided outside a fuel injection pump and the second control unit is provided inside the fuel injection pump, and data of a desired fuel injection quantity and data of a desired fuel injection timing calculated in the first control unit are transferred to the second control unit by interrupt processing, and the second control unit on one hand receives both the data and on the other hand is interrupted by pulses generated in accordance with the rotation of a camshaft of the fuel injection pump whereby the second control unit calculates driving timing of a solenoid valve which effects opening and closing of a fuel injection valve, by the use of the data of the desired fuel injection quantity and the data of the desired fuel injection timing, and data of a rotational speed and a rotational angular position of the camshaft of the fuel injection pump which are detected based on the above-mentioned pulses, and sends out a signal based on results of the calculation for driving the solenoid valve.
However, according to such a construction of the conventional system, no consideration has been given to the relationship between the period of transfer of data from the first control unit to the second control unit and the period of interruption of the second control unit by pulses generated in accordance with the rotation of the camshaft of the fuel injection pump. Therefore, if the period of transfer of data and the period of interruption by the pulses continuously coincide with each other, and if the interrupt processing for reception of the data and the interrupt processing responsive to the pulses, both of which are to be carried out in the second controll unit, coincide with each other, the time will not come when the interrupt processing for reception of the data is carried out.